Process for protection of metallic surfaces



Patented J an. 5, 1926.

g 4 A 1,568,728- umrao 'STAT'ES PATENT, ounce.

GEORGE c. FREEMAN, or PHILA ELPHIA, PENNsYLvANIA, ASSIGNOR 'roAN'rIscALa CORPORATION, OF PHILADELPHIA, PENNSYLVANIA, A CORPORATION OFDELA- WARE.

No Drawing To all whom it my-concem:

1 Be it'k'nown that I, Gnonon C. FREEMAN, a citizen of the UnitedStates, and resident of Philadelphia, in the countyof Philadelphia andState of Pennsylvania, have invented new and useful Improvements inProcesses. for Protection of Metallic Surfaces, 'of which the followingis a specification.

My invention relates to a method'of preventing or eliminating thescaling or encrusting of metal in contact with fluid, a

- special and important embodiment and application ofmy invention beinga method whereby containers or conduits such as boilers, evaporators,economizers, condensers, cold and hot water pipes and the like areprotected against the; "formation of scale fromsediment or precipitatesin the fluid therein contained and being processed.

The fact that scale or encrustation forms upon metallic surfaces thatare in contact I with fluid, particularly when the fluid is undergoing'achangeof character or temperature is wellvl mo'w n and the fact thatunder such condition electrolytic corrosion of the metal takes-placeisalso well known, such corrosion being Hereinafter referred to as normalor natural electrolytic corrosion,- an example thereof being the rustingor pit= ting of a steam boiler,

' It has heretofore been proposed to protect a metallic surface that isin contact with a fluid against the formation of scale or en- Icrustation by passing an electric current through'the metallic body ofWhlCh the surface is to be protected, or by Introducing the current tothe metallicbody and withdrawing it from the fluid or. vice versa.- And,it 1 has been proposed heretofore to employ elec: tric current of lowvoltage. In the practice of my invention I prefer to introduce anelectric current to and withdraw it from the metallic bod of which thesurface is to be protected .w1thout directly introducing thezcurrent toor withdrawing it from the,

that is in contact with that surface. ln 'ofrder, to effect theprerentlon and ellml- I nationgof the formation and adhesion of scale'aiid.encrustation upon'the surface of the metallic body that is. incontact Wltll a' r fluid the voltage of the'current that is passedthrough themetallic body and the amount of current flowing through themetalllc body are carefully regulated, The voltage of that rnocnss roaPROTECTION or METALLiC suar'AcEs:

Application filed April' 13, 1925. Serial 1T0. 22,879.

current is so regulated that the natural or normal electrolyticcorrosion of that surface will not be appreciably augmented or accel--erated, and the current is so regulated that scaling and encrustation ofthe surface to be protected are prevented and eliminated. To

this end the terminals of a source of electric current are connected toremote points of the metallic body of which the'surface' is to beprotected against the formation and ad- 'hesion of scale andencrustation. The poten lytic corrosion of the surface will not bethereby appreciably accelerated or augmented. If the surface tobeprotected is of such form that points widely spaced along that surfaceare nevertheless in such proxim ity that current might flow through thefluid between those two points, the points of the surface which are tobe connected with the terminals of the source of current are so selectedas to avoid sucli straying or diversion of the current through thefluid. The value of the potential gradient that may be maintained alongthe extent of the body of which the surface is to be protected will varywith the conditions to. which that surface is subjected. Theconductivity of the fluid in contactwith the surface to be protected,the character of that fluid, for example, the chemical activity thereofwith respect to the surface to be protected, the temperature of thesurface. to be protected, and the proximity or portions of the surfaceare conditions that may control the value of thepotential gradient thatmust be employed and the points at which the source 0 connected thereto.In determining the proper potential gradient to be used, under theparticular conditions surrounding the surface to be protected, and thepoints at which the source of electric current is to be connected tothat surface, the controlling factor current is to be is that then'drma'l or natural electrolytic" corrosion shall not be c appreciablyau 5 mented or accelerated beyond that whic' would take place if noelectric current from i an external source were passed through the bodyof which the surface is to be protected. The potential gradient havingbeen ascertained the amount of current passing through the metallic bodyof which the surface is to be protected is'to be brought to such valuethat formation and adhesion ofscale or encrustation will ordinarily beprevented and in most cases previously formed scale will be removed. Theamount of current flowing through the body of which the surface is to beprotected is not to be determined by a measurement of only the amount ofcurrent flowing but is to be determined by ratio of that current to thecross-sectional area of the metallic body of which the surface is to beprotected. In other words it is the crosssectional density of thecurrentthat is the measure by which the amount of current is to be regulated;If it be found that with a given potential gradient a certain amount ofcurrent will protect the surface of ,a given metallic body the currentnecessary to protect the surface of another metallic body of a similarmetal under the same conditions must be such that the cross-sectionaldensity of the current is substantially the same in both bodies. i

4 I have found that certain metallic bodies of which the surface is tobe protected, for example, a steam boiler, have a current flowingthrough them, which will be referred to herein as the inherent currentof the body, and which may result from a thermo-electric, orthermo-couple effect, in the metalhc body itself, by reasonof'variations 1n the temperature and chemical composition throughout themetallic body, or. from galvanic action due to contact of the metal withliquid, or from some other cause. I have found that the flow in ametallic body of which the surface is to be protected of suflicientcurrent to produce a cross-sectional density of current great enough toprotect that surface, will be enhanced if the current produced by anexternal source between the points at which the terminals of that sourceare connected, flows in the same direction as the inherent current ofthe metallic body. In accordance with my-invention the direction of flowis determlned of such inherent current, if any, between the points atwhich the terminals of the external source of cur-" the formation and aesion of scale and encrustation while maintaining the potential must beemployed in order to protect that 7 surface against the formation andadhesion of scale and encrustation, and also of the direction in whichcurrent from an external source must be caused to flow within the bodyof which the surface is to be protected in order that a sufficientcross-sectional density of current may be produced without theemployment of a potential gradient that will accelerate or augment thenatural or rormal corrosion of the. surface to be protected. As anexample I have found that the protection of a,steam boiler of the usualboiler steel and'containing water of ordinary hardness, may beaccomplished if the potential gradient is equal to, or less than, onemilli-volt per linear foot of the boiler and the cross-sectional'densityof the current is equal to or greater than one third of a milli-ampereper square inch of the crosssection of the metal of the boiler, providedthe external source of current is connected tothe boiler, in accordancewith my invention, so that the inherent current of the boiler and thecurrent supplied from the external source flow in the same direction.The thermo-couple is a convenient and desirable source of electriccurrent for use in the practice of my invention.v In the example abovereferred to remotely spaced points on the boiler, namely at the ends,were so selected that by connecting the terminals of a thermo-couple tothose points there would be a substantially uniformv flow of currentthroughout all parts of the metallic boiler shell and by connecting thelead wires of a volt meter to those points .a deflection of theindicating needle of the volt meter indicated that there was an inherentflow of current in the boiler shell .between those points due possiblyto thermo-electric action within the boiler or to differences in thematerial of different arts of the boiler or to galvanic action wit inthe boiler or to other causes. The junctionof the thermo-couple wasfastened in close contact with a'heated connections between theterminals of the thermo-couple and the selected points on the boilerwere reversed and the current in the manner that caused the greatestflow of current I was assured that the current flowing in the boilershell from the thermocouple was flowing in the same direction as theinherent current of the boiler of which the existence was indicated bythe fact that the needle of a volt meter connected between lhosepointswas deflected. v

What I claim and desire to secure byLetters Patent of the United Statesis:

1. The process of protecting a fluid-contacting-surface of a metallicbody against encrustation or scaling which comprises so' connecting theterminals of a source of electric current to spaced points of said bodythat current is caused by said source of current to flow in said body inthe same direction'as. the inherent current in said body.

2. The process of protecting a fluid-contacting surface of a metallicbody against encrustation or scaling which comprises connecting theterminals of a source of electric current to spaced points of said bodyand thereby completing an electric circuit including a part of saidbody, and so regulating the direction of current flowing from saidsource that current from said source produces in said b'od between saidpoints a flow of current in the same direction as the inherent currentin said body.

3. The process of protecting a flHld-C011 tacting surface of a metallicbody against encrustation or scaling which comprises causing electriccurrent from an external source to flow through said body in the samedirection as the inherent current in said body.

4. The process of protecting a fluid-contacting surface of a metallicbody against encrustation or scaling which comprises connecting theterminals of a source of electric current to spaced points of said bodyand thereby completing an electric circuit including a part of saidbody, and so regulating the direction of current flowing from saidsource that current from said source produces in said body between saidpoints a flow of current in the same direction as the inherent currentin said body, while main taining the potential gradient between saidpoints below that which Will accelerate normal electrolytic corrosion ofthe surface.

5. The process of protecting a fluid-contacting surface of a metallicbodypagainst encrustation or scaling which comprises causing electriccurrent, from an external source to flow through said body 1n the samedirection as the inherent current in said body, while maintaining thepotential gradient between said points below that which will acceleratenormal electrolytic corrosion of the surface.

In testimony whereof, I have signed my name to this specification.

' GEORGE C. FREEMAN.

